This invention relates to valves, particularly those valves employed in fuel injection systems for internal combustion engines. More particularly, the valves of the invention use the change in dimensions of a piezoelectric element to effect movement of a valve needle from a closed position to an open position.
It is known that upon application of an electrical field across piezoelectric materials they expand or contract along known axes, depending on the direction in which the electrical field is applied. It is further known to stack a number of piezoelectric elements so that their cumulative expansion or contraction effect provides an increased mechanical movement. It is also known that piezoelectric elements having these expanding and contracting properties can be used to pump fuel from an injector by alternating an imposed electric field at suitable intervals. For example, Benson in U.S. Pat. No. 3,391,680 describes such a pump where the piezoelectric element is used to pressurize the fuel.
The present invention does not relate to a piezoelectric actuated pump wherein the piezoelectric element pressurizes and pumps the fuel but rather relates to a valve for precise metering and control of small quantities of an already pressurized fluid.
In conventional fuel injection systems, high pressure, timed metering pump systems are used with relatively inexact timing and with non-uniform injected amounts of fuel. These are especially unsuitable for diesel engines and result in incomplete combustion which in turn increases adverse effects including both air and noise pollution.
In a copending commonly assigned patent application by Hans U. Bart, Ser. No. 509892, filed 4/3/75 there is disclosed an improved fuel injector valve wherein a close control of the timing, the amount of fuel injected and the number of injections is possible. A valve body is supplied with fuel under pressure, e.g. about 6000 psi. The fuel is normally held in the valve body by a normally closed injector port which is maintained closed by a needle or other valve closure means seated in the port. A piezoelectric element cooperates with the needle in a manner such that the imposition of an electric field across the element changes its dimensions, either expanding it or contracting it, and effects movement of both the element and the needle. The latter movement opens the valve port permitting the pressurized fuel to jet therefrom.
The invention disclosed in said copending patent application also provides a mechanical or hydraulic amplification means to magnify the stroke of the piezoelectric element to lift, for example, the needle closing the valve opening. Such a valve is exceedingly fast and capable of response within microseconds, making it particularly suitable for injection control of diesel engines. The injector valve disclosed therein thus provides a combination of control flexibility and instantaneous response.